Arcuate rolling bearing

ABSTRACT

A bearing for a ball-shaped gimbal ring of a gimbal system has opposing arcuate tracks mounted individually to a gimbal ring and a base of the system. In a first embodiment, a ring track is segmentally opposed by a base track. Balls are disposed within the ring track and are kept there by a cage and retainer. A second embodiment includes a gimbal ring track that is fully opposed by the base track. Caged balls partially fill these tracks so that the balls are constantly opposed by the tracks in spite of differences in track and ball speeds.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains generally to gimbal systems of the type used tosupport antenna units. More particularly, the invention relates to abearing used to support the gimbal rings of such systems.

2. Description of the Prior Art

In many applications, it is important that a platform maintain a preciseorientation irrespective of the movements of the platform's support.Traditionally, this has been accomplished by mounting the platformwithin a concentric arrangement of inner and outer gimbal rings. Typicalgimbal systems of this sort include a mounting base, an outer gimbalring rotatably attached to the mounting base, and an inner gimbal ringrotatably attached to the outer ring for rotation about an axis that isperpendicular to the rotational axis of the outer ring. This structureallows a platform attached to the inner ring to stabilize, or maintainits line of sight, even though the support of the platform is unsteady.The limits of this line of sight define a "look angle", determined bythe shape of the outer gimbal ring. The shape of the outer ring is,among other things, dictated by the bearing used to attach it to themounting base. This bearing must not only allow the inner gimbal ringand platform to be able to swing through a large look angle, but, in thecase in which sensitive electronics are involved, must also provide anextremely steady, low vibration coupling to the outer ring base.

There are numerous prior art bearing designs for maintaining precisiongimbal ring alignment and movement. They all, however, have certaindeficiencies. Current methods of aligning the outer gimbal ring involvethe use of bearing races which are a part of the outer edges of thegimbal ring itself. A common scheme is to allow the outer ring to rideupon several relatively large rollers. The effect of this design is aconcentration of vibrational and other loadings over a small segment ofthe ring. Another prior art method is to fashion a recirculating bearingpath in the platform base. The path is positioned to allow circulatingballs to contact bearing races on the outer edges of the gimbal ring.Dimensional limitations require the balls to negotiate tight corners,lessening the smoothness of the gimbal ring movement.

SUMMARY OF THE INVENTION

The invention provides a bearing for rotatably supporting a gimbal ringof a gimbal system. The bearing permits the gimbal ring to rotate aboutan axis; therefore as used herein, "axially" means in a direction alongan axis about which such a gimbal ring rotates or pivots in relation toa base for the ring. Though the bearing is used in pairs, only a singlebearing will be discussed and the reader may assume that what applies toone bearing applies equally to the other.

A first embodiment includes a first circularly arcuate race mounted toan axially facing edge of a generally bail-shaped gimbal ring. Thisfirst race defines a first axially facing bearing track. A plurality ofballs are disposed in rolling engagement with the first track of thisfirst race. A cage is used to hold and separate the balls withoutobstructing their contact with the first track. Guide members aremounted to opposite sides of this cage. Coaxially mounted to the firstrace are shoulders defining opposing, radially extending grooves. Theguide members slideably engage these grooves to keep the cagesubstantially adjacent to the first race and the balls in substantiallyconstant contact with the first track. A second circularly arcuate raceis attached to a base of the gimbal system. The second race defines asecond axially facing bearing track of the same radius as the firsttrack. This second track is positioned in opposing relationship to thefirst track, however the second track opposes only a portion or segmentof the first track. A number of balls are disposed in rolling engagementbetween the opposing first and second tracks, while other unopposedballs continue within the first track beyond the ends of the secondtrack. The unopposed balls are kept in the first track by the cagemember and grooved shoulder structures previously mentioned and serve toprovide a continuous rolling surface between the gimbal ring and thebase as the gimbal ring rotates with respect to the base.

A second embodiment also includes a first circularly arcuate race. Thefirst race is attached to an axially facing edge of a generallybail-shaped gimbal ring. The first race defines a first axially facingbearing track. A plurality of balls are disposed in rolling engagementwith this first track. These balls are held and separated by a ballcage. A second circularly arcuate race defining a second axially facingbearing track is attached to a base of the gimbal system. This secondtrack has the same radius as the first track, and is positioned inopposing relationship to the first track so that the balls are rollablyengaged and the cage is slideably engaged between the two tracks. Thefirst and second tracks extend beyond the ball cage so that, as thegimbal ring is rotated with respect to the base, any advancing balls areretained within the races and the need for cage keeper structure isavoided.

Each of these embodiments allow rotational and other loads to bedistributed over relatively large bearing interfaces, thus making smoothand precise gimbal ring movement possible.

OBJECTS OF THE INVENTION

A primary object of this invention is to provide a bearing suitable forgimbal ring mounting applications.

Another object of the invention is to provide a gimbal ring bearing thatpermits large look angles for a gimballed platform effectively attachedthereto.

Yet another object of the invention is to provide a gimbal ring bearingthat can maintain smooth and precise operation while experiencing highloads and intense vibration.

These and other objects will become apparent when the followingspecification, drawings and claims are construed together.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a representative gimballed platformincluding a first embodiment of the invention.

FIG. 2 is a cross-section of bearing interfaces of the embodiment shownin FIG. 1.

FIG. 3 is a perspective view of a portion of the cage used in theembodiment shown in FIGS. 1 and 2.

FIG. 4 is an isometric view of a gimbal ring and base cut away to show asecond embodiment of the invention.

FIG. 5 is a cross-section of bearing interfaces of the embodiment shownin FIG. 4.

FIG. 6 is perspective view of a portion of the cage used in theembodiment shown in FIGS. 4 and 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

FIG. 1 is a view of a representative gimbal system 10 having an arcuaterolling bearing 11 which is a first embodiment of the subject invention.System 10, typically, has an antenna 12 attached to a platform 14.Platform 14 is in turn attached to an inner gimbal ring 16. Inner ring16 is mounted for rotation within an outer bail-shaped gimbal ring 18 bya pair of bearings 20 each of which rotationally receives an extension21 of ring 16, only one of these bearings and the correspondingextension being shown in FIG. 1. Outer ring 18 rotates about an axis 19,which is defined by arcuate bearing 11, and has an edge 22 facingaxially thereof. Bearing 11 has a first circularly arcuate race 24 thatis fixedly mounted to edge 22 by adhesive bonding or any other suitableattachment means. First race 24 has a first axially facing bearing track26. Disposed in rolling engagement with first track 26 is a plurality ofrolling elements, such as balls 28, conventional in the bearing art.Balls 28 are held and separated by an arcuate cage 30, and are kept insubstantially constant contact with first track 26 by structure to bediscussed in greater detail. A second circularly arcuate race 32 isfixedly mounted to a base 34 by any suitable attachment means such asadhesive bonding. Races 24 and 32 are made of any suitable material.Second race 32 has a second axially facing bearing track 36, best shownin FIG. 2, of the same radius as first track 26. Second track 36segmentally opposes first track 26, "segmentally" as so used hereinmeaning that second track 36 opposes only a portion or segment of firsttrack 26. A number of the balls 28 are rollingly engaged between firsttrack 26 and second track 36. The remainder of balls 28 continue withinthe first track 26 beyond the second track 36. These remainder ballsprovide a continued rolling surface for rotation of the gimbal ring withrespect to the base, and are retained in the first track by structure tobe hereafter discussed.

FIG. 2 is a cross-section of bearing interfaces of the inventiveembodiment shown in FIG. 1. One of the balls 28 is shown disposedbetween first race 24 and second race 32 in rolling engagement withfirst track 26 and with second track 36. First track 26 and second track36 are of a well-known Gothic arch shape to provide a four-point contactsurface; however, a variety of track configurations may be used as iswell understood in the bearing art. Bearing 11 has an inner shoulder 38and an outer shoulder 40 which are mounted to first race 24 and arecoaxial therewith in relation to axis 19 which is shown in FIG. 1.Shoulders 38 and 40 and race 24 may be unitarily constructed or, as isshown, the shoulders may be made independently of the race and then beattached thereto. Inner shoulder 38 is positioned at a lesser radiusmeasured from axis 19 than the radius at which outer shoulder 40 ispositioned. With respect to axis 19, inner shoulder 38 has a radiallyouter surface 42, and outer shoulder 40 has a radially inner surface 44facing outer surface 42 and coaxial thereto. Outer surface 42 has aradially inwardly extending inner groove 46, and in like but oppositemanner, inner surface 44 has a radially outwardly extending outer groove48.

Referring to FIGS. 2 and 3, it can be seen that cage 30 is configured soas to separate and hold balls 28 while permitting them to rollinglyengage tracks 26 and 36. Cage 30 is swaged, as indicated by numeral 49in FIG. 3, or is machined to hold balls 28 tightly enough to keep theballs for falling out of the cage but loosely enough to permit them torotate freely within the cage. Cage 30 is typically made of a softmetal; however, those skilled in the art will realize that a cage ofnon-metallic material, such as oil-impregnated "Micarta", may also beused. As is shown in FIGS. 2 and 3, a first radially extending guidemember 50 is fixedly mounted to cage 30. A second radially extendingguide member 52 is also fixedly mounted to cage 30 and is positionedopposite thereof from first member 50. The guide members and the cagemay be unitarily constructed, or the members may be manufacturedseparately of the cage and then attached thereto. As is shown in FIG. 2,first member 50 extends into inner groove 46 for slideable engagementtherewith. Similarly, second member 52 extends into outer groove 48 forslideable engagement therewith.

Referring again to FIGS. 1 and 2, operation of the invention is suchthat, as gimbal ring 18 rotates with respect to base 34, a continuedrolling surface is maintained between first track 26 of first race 24,and second track 36 of race 32. Those of balls 28 that are initiallyunopposed by the second track 36 may become rollingly engaged betweentracks 36 and 26 as gimbal ring 18 rotates. Any difference between trackand balls speeds is thus compensated for. As ring 18 rotates, those ofballs 28 that become unopposed by second track 36 are retained in firsttrack 26 since cage 30 is configured to hold balls 28 and guide members50 and 52, which are fixedly mounted to cage 30, slideably engagegrooves 46 and 48, respectively, and keep cage 30 substantially adjacentfirst race 24 and first track 26.

Second Embodiment

FIG. 4 shows a portion of a gimbal system, of the general type shown inFIG. 1, having an arcuate bearing 98 which is a second embodiment of thesubject invention. The gimbal system includes an outer bail-shapedgimbal ring 100 rotatably mounted to a base 102.

Referring to both FIGS. 4 and 5, gimbal ring 100 rotates about an axis103, shown in FIG. 4, and has an axially facing edge 104. Bearing 98 hasa first circularly arcuate race 106 that is fixedly mounted to edge 104by adhesive bonding or any other suitable attachment means. First race106 has a first axially facing bearing track 108. Disposed in rollingengagement with first track 108 is a plurality of rolling elements, suchas balls 110, conventional in the bearing art. Balls 110 are held andseparated by an arcuate cage 112 to be described in greater detail. Asecond circularly arcuate race 114 is fixedly mounted to secondcircularly arcuate race 114 is fixedly mounted to the base 102 by anysuitable attachment means such as adhesive bonding. Races 106 and 114are made of any suitable material. As is best shown in FIG. 4, secondrace 114 has a second axially facing bearing track 116 of the sameradius as first track 108. Second track 116 opposes first track 108 sothat balls 110 are rollingly engaged between tracks 108 and 116. Firsttrack 108 and second track 116 are of a well-known Gothic archconfiguration to provide a four-point contact bearing surface, howeverother track configurations may be used. Cage 112 is slideably engagedbetween first race 106 and second race 114, and permits balls 110 torollingly contact tracks 108 and 116 as well be described.

Referring to FIGS. 5 and 6, it can be seen that cage 112 holds andseparates balls 110 while permitting the balls to rollingly engageadjacent bearing tracks 108 and 116. Cage 112 may be swaged, as depictedin FIG. 6, or may be machined to hold balls 110 tightly enough to keepthe balls from falling out of the cage but loosely enough to permit themto rotate freely within the cage. However, cage 112, unlike cage 30 ofbearing 11 of the first embodiment, need not be so configured sinceballs 110 are kept within cage 112 by the adjacent bearing tracks 108and 116. Cage 112 is, preferably, made of a soft metal; however, thoseskilled in the bearing art will realize that a cage of non-metallicmaterial may also be used.

Referring again to FIG. 4, it can be seen that first track 108 andsecond track 116 extend beyond ball cage 112 so that, as gimbal ring 100is rotated with respect to base 102, balls 110 are retained within thetracks. Differences in ball and track speeds are thus compensated for bythese additional lengths of track.

For both embodiments of the invention, constructing the gimbal ring andbase of suitable bearing material would allow the tracks of the bearingto be cut directly into these gimbal system components, rather thanattaching the tracks thereto. Furthermore, it should be understood thatthough the invention has been described for use with the outer gimbalring of a gimbal system, the invention may be used with inner gimbalrings in which the adjacent outer ring would served as a base.

Obviously, those skilled in the art will realize that these and othermodifications and variations of the invention are possible in light ofthe above teachings. Therefore, it is to be understood that within thescope of the following claims the invention may be practiced otherwisethan as specifically described.

What is claimed is:
 1. A rolling bearing comprising:a first circularlyarcuate race defining a first axially facing bearing track; a pluralityof rolling elements disposed in rollable engagement with said firsttrack; cage means for holding said rolling elements and for separatingsaid rolling elements from each other; and a second circularly arcuaterace defining a second axially facing bearing track having the sameradius as said first track and being axially opposed thereto so thatsaid second track is rollably engaged with said elements.
 2. The bearingof claim 1 in which said cage means is slideably engaged between saidfirst race and said second race.
 3. The bearing of claim 1 in which saidsecond track segmentally opposes said first track so that a number ofsaid rolling elements are rollably engaged with said second track. 4.The bearing of claim 3 further comprising means for slideably keepingsaid cage substantially adjacent to said first race so that said rollingelements are retained in said first track.
 5. A rolling bearing forrotatably supporting a gimbal ring of a gimbal system upon a base ofsaid system, said gimbal ring being rotatable about an axis and havingan axially facing edge, the bearing comprising:a first circularlyarcuate race mounted to said edge of said gimbal ring, said first racedefining a first axially facing bearing track; a plurality of rollingelements disposed in rollable engagement with said first track; a cagefor holding said rolling elements and for separating said rollingelements from each other; and a second circularly arcuate race defininga second axially facing bearing track having the same radius as saidfirst track and being axially opposed thereto so that said second trackis rollably engaged with said elements.
 6. The bearing of claim 5 inwhich said cage is disposed in slideable engagement between said firstrace and said second race.
 7. The bearing of claim 5 in which saidsecond track segmentally opposes said first track so that a number ofsaid rolling elements are rollably engaged with said second track. 8.The bearing of claim 7 further comprising means for slideably keepingsaid cage substantially adjacent to said first race so that saidplurality of rolling elements are retained in said first track.
 9. Thebearing of claim 8 in which said keeping means includes:an innershoulder and an outer shoulder which are coaxially mounted to said firstrace, said inner shoulder being positioned at a lesser radius measuredfrom said axis than the radius at which said outer shoulder ispositioned, said inner shoulder defining a radially inwardly extendinginner groove and said outer shoulder defining a radially outwardlyextending outer groove facing said inner groove; and a first guidemember and a second guide member which are oppositely mounted to saidcage, said first member extending into said inner groove for slideableengagement therewith and said second member extending into said outergroove for slideable engagement therewith so as to slideably keep saidcage substantially adjacent said first race so that said plurality ofrolling elements are retained in said first track.
 10. A four-pointcontact ball bearing for supporting a generally bail-shaped gimbal ringof a gimbal system upon a base of said system, said gimbal ring beingrotatable about an axis and having an axially facing edge, said bearingcomprising:a first circularly arcuate race mounted to said axial edge ofsaid gimbal ring, said first arcuate race defining a first axiallyfacing bearing track; a plurality of balls disposed in rollableengagement with said first track; an arcuate cage for holding said ballsand separating said balls from each other, said cage having opposite,radially extending first and second guide members; means for slideablykeeping said cage substantially adjacent to said first race so that saidplurality of balls are retained in said first track, said keeper meanshaving:an inner shoulder and an outer shoulder which are coaxiallymounted to said first race, said inner shoulder being positioned at alesser radius measured from said axis than the radius at which saidouter shoulder is positioned, said inner shoulder defining a radiallyinwardly extending inner groove and said outer shoulder defining aradially outwardly extending outer groove facing said inner groove,where said first guide member of said cage extends into said first innergroove for slideable engagement therewith and said second guide memberof said cage extends into said outer groove for slideable engagementtherewith; and a second circularly arcuate race mounted to said base anddefining a second axially facing bearing track having the same radius assaid first track and being segmentally opposed thereto so that a numberof said balls are rollably engaged with said second track.
 11. Thebearing of claim 1 in which said first track of said first circularlyarcuate race and said second track of said second circularly arcuaterace extend beyond said cage containing said plurality of rollingelements so that said plurality of rolling elements are retained withinsaid tracks when said tracks are rotated with respect to each other. 12.The bearing of claim 5 in which said first track of said firstcircularly arcuate race and said second track of said second circularlyarcuate race extend beyond said cage containing said plurality ofrolling elements so that said plurality of rolling elements are retainedwithin said tracks when said tracks are rotated with respect to eachother.
 13. A rolling bearing for rotatably supporting an outer gimbalring of a gimbal system upon a base of said system, said gimbal ringbeing partial, stopped rotatable about an axis and having an axiallyfacing edge, the bearing comprising:a first arcuate race having acircular shape and concentric with said axis mounted to said edge ofsaid gimbal ring, said first race defining a first axially facingbearing track; a plurality of rolling elements disposed in rollingengagement with said first track; a cage for holding said rollingelements and for separating said rolling elements from each other; and asecond circularly shaped arcuate race mounted to said base of saidgimbal system, said second race defining a second axially facing bearingtrack having the same radius as said first track and being axiallyopposed thereto so that said second track is rollably engaged with saidrolling elements, said first track of said first circularly arcuate raceand said second track of said second circularly arcuate race beingextended beyond said cage containing said plurality of rolling elementsso that said plurality of rolling elements are retained within saidtracks when said tracks are rotated with respect to each other.